Linear Equations

linear equations class 8 rs aggarwal

Step by Step solutions of Exercise- 15A of RS Aggarwal ICSE Class-8 Maths chapter 15- Linear Equations by Goyal Brothers Prakashan is provided.

Table of Contents

Exercise-15A

Q1: Solve \(4x – 9 = 2x + 7\)

Step 1: Write the given equation: \[ 4x – 9 = 2x + 7 \]Step 2: Transpose \(2x\) to the left-hand side and \(-9\) to the right-hand side: \[ 4x – 2x = 7 + 9 \]Step 3: Simplify both sides: \[ 2x = 16 \]Step 4: Divide both sides by 2: \[ x = \frac{16}{2} = 8 \]Answer:x = 8


Q2: Solve \(5y + 18 = 11 – 2y\)

Step 1: Write the given equation: \[ 5y + 18 = 11 – 2y \]Step 2: Transpose \(-2y\) to the left-hand side and 18 to the right-hand side: \[ 5y + 2y = 11 – 18 \]Step 3: Simplify both sides: \[ 7y = -7 \]Step 4: Divide both sides by 7: \[ y = \frac{-7}{7} = -1 \]Answer:y = -1


Q3: Solve \(21 – 3(x – 7) = x + 20\)

Step 1: Write the given equation: \[ 21 – 3(x – 7) = x + 20 \]Step 2: Expand the bracket: \[ 21 – 3x + 21 = x + 20 \\ 42 – 3x = x + 20 \]Step 3: Transpose \(x\) to the left-hand side and 42 to the right-hand side: \[ -3x – x = 20 – 42 \\ -4x = -22 \]Step 4: Divide both sides by -4: \[ x = \frac{-22}{-4} = \frac{22}{4} = \frac{11}{2} \]Answer:x = \(\frac{11}{2}\)


Q4: Solve \(3(y-7)-2(3y-4) = (2-5y)\)

Step 1: Write the given equation: \[ 3(y – 7) – 2(3y – 4) = 2 – 5y \]Step 2: Expand the brackets: \[ 3y – 21 – 6y + 8 = 2 – 5y \\ -3y – 13 = 2 – 5y \]Step 3: Transpose \(-5y\) to the left-hand side and \(-13\) to the right-hand side: \[ -3y + 5y = 2 + 13 \\ 2y = 15 \]Step 4: Divide both sides by 2: \[ y = \frac{15}{2} \]Answer:y = \(\frac{15}{2}\)


Q5: Solve \(3(t-5)-16t = 12 – 2(t-3)\)

Step 1: Write the given equation: \[ 3(t – 5) – 16t = 12 – 2(t – 3) \]Step 2: Expand the brackets: \[ 3t – 15 – 16t = 12 – 2t + 6 \\ -13t – 15 = 18 – 2t \]Step 3: Transpose \(-2t\) to the left-hand side and \(-15\) to the right-hand side: \[ -13t + 2t = 18 + 15 \\ -11t = 33 \]Step 4: Divide both sides by -11: \[ t = \frac{33}{-11} = -3 \]Answer:t = -3


Q6: Solve \(\frac{3x}{4} – \frac{(x-4)}{3} = \frac{5}{3}\)

Step 1: Write the given equation: \[ \frac{3x}{4} – \frac{(x-4)}{3} = \frac{5}{3} \]Step 2: Take LCM of denominators 4 and 3 for the left-hand side: LCM = 12 \[ \frac{9x}{12} – \frac{4(x-4)}{12} = \frac{5}{3} \\ \frac{9x – 4(x-4)}{12} = \frac{5}{3} \]Step 3: Simplify numerator: \[ 9x – 4x + 16 = 5x + 16 \\ \frac{5x + 16}{12} = \frac{5}{3} \]Step 4: Cross multiply: \[ 3(5x + 16) = 12 \cdot 5 \\ 15x + 48 = 60 \]Step 5: Simplify: \[ 15x = 60 – 48 \\ 15x = 12 \\ x = \frac{12}{15} = \frac{4}{5} \]Answer:x = \(\frac{4}{5}\)


Q7: Solve \(\frac{4x+1}{3} + \frac{2x-1}{2} – \frac{3x-7}{5} = 6\)

Step 1: Write the given equation: \[ \frac{4x+1}{3} + \frac{2x-1}{2} – \frac{3x-7}{5} = 6 \]Step 2: Take LCM of denominators 3, 2, 5 for the left-hand side: LCM = 30 \[ \frac{10(4x+1)}{30} + \frac{15(2x-1)}{30} – \frac{6(3x-7)}{30} = 6 \\ \frac{10(4x+1) + 15(2x-1) – 6(3x-7)}{30} = 6 \]Step 3: Expand numerators: \[ \frac{40x + 10 + 30x – 15 – 18x + 42}{30} = 6 \\ \frac{(40x + 30x – 18x) + (10 – 15 + 42)}{30} = 6 \\ \frac{52x + 37}{30} = 6 \]Step 4: Multiply both sides by 30: \[ 52x + 37 = 180 \]Step 5: Simplify: \[ 52x = 180 – 37 \\ 52x = 143 \\ x = \frac{143}{52} = \frac{143 \div 13}{52 \div 13} = \frac {11}{4} \]Answer:x = \(\frac{11}{4}\)


Q8: Solve \(\frac{z+5}{6} – \frac{z+1}{9} = \frac{z+3}{4}\)

Step 1: Write the given equation: \[ \frac{z+5}{6} – \frac{z+1}{9} = \frac{z+3}{4} \]Step 2: Take LCM of denominators 6, 9, 4 for the left-hand side: LCM = 36 \[ \frac{6(z+5) – 4(z+1)}{36} = \frac{z+3}{4} \]Step 3: Simplify numerator: \[ \frac{6z + 30 – 4z – 4}{36} = \frac{2z + 26}{36} = \frac{z+13}{18} \\ \frac{z+13}{18} = \frac{z+3}{4} \]Step 4: Cross multiply: \[ 4(z+13) = 18(z+3) \\ 4z + 52 = 18z + 54 \]Step 5: Simplify: \[ 4z – 18z = 54 – 52 \\ -14z = 2 \\ z = -\frac{2}{14} = -\frac{1}{7} \]Answer:z = -\(\frac{1}{7}\)


Q9: Solve \(\frac{2-9z}{17-4z} = \frac{4}{5}\)

Step 1: Write the given equation: \[ \frac{2-9z}{17-4z} = \frac{4}{5} \]Step 2: Cross multiply: \[ 5(2-9z) = 4(17-4z) \]Step 3: Expand both sides: \[ 10 – 45z = 68 – 16z \]Step 4: Transpose terms: \[ -45z + 16z = 68 – 10 \\ -29z = 58 \]Step 5: Divide both sides by -29: \[ z = \frac{58}{-29} = -2 \]Answer:z = -2


Q10: Solve \(\frac{2x-3}{3x-1} = \frac{2x+3}{3x+4}\)

Step 1: Write the given equation: \[ \frac{2x-3}{3x-1} = \frac{2x+3}{3x+4} \]Step 2: Cross multiply: \[ (2x-3)(3x+4) = (2x+3)(3x-1) \]Step 3: Expand both sides: \[ 6x^2 + 8x – 9x – 12 = 6x^2 – 2x + 9x – 3 \\ 6x^2 – x – 12 = 6x^2 + 7x – 3 \]Step 4: Transpose terms to bring all variables to one side: \[ 6x^2 – x – 12 – 6x^2 – 7x + 3 = 0 \\ -8x – 9 = 0 \]Step 5: Solve for x: \[ -8x = 9 \\ x = -\frac{9}{8} \]Answer:x = -\(\frac{9}{8}\)


Q11: Solve \(\frac{2-9x}{16+5x}=0\)

Step 1: Write the given equation: \[ \frac{2-9x}{16+5x} = 0 \]Step 2: A fraction is zero when its numerator is zero: \[ 2 – 9x = 0 \]Step 3: Solve for x: \[ -9x = -2 \\ x = \frac{2}{9} \]Answer:x = \(\frac{2}{9}\)


Q12: Solve \(\frac{0.5z+4}{1.2z+6} = \frac{5}{3}\)

Step 1: Write the given equation: \[ \frac{0.5z + 4}{1.2z + 6} = \frac{5}{3} \]Step 2: Cross multiply: \[ 3(0.5z + 4) = 5(1.2z + 6) \]Step 3: Expand both sides: \[ 1.5z + 12 = 6z + 30 \]Step 4: Transpose terms: \[ 1.5z – 6z = 30 – 12 \\ -4.5z = 18 \]Step 5: Divide both sides by -4.5: \[ z = \frac{18}{-4.5} = -4 \]Answer:z = -4


Q13: Solve \(\frac{3}{2x-1} + \frac{4}{2x+1} = \frac{7}{2x}\)

Step 1: Write the given equation: \[ \frac{3}{2x-1} + \frac{4}{2x+1} = \frac{7}{2x} \]Step 2: Take LCM of the denominators \((2x-1)(2x+1)(2x)\) to eliminate fractions: \[ 3 \cdot 2x \cdot (2x+1) + 4 \cdot 2x \cdot (2x-1) = 7 \cdot (2x-1)(2x+1) \]Step 3: Expand each term: \[ 3(2x)(2x+1) = 12x^2 + 6x \\ 4(2x)(2x-1) = 16x^2 – 8x \\ 7(2x-1)(2x+1) = 7(4x^2 – 1) = 28x^2 – 7 \]Step 4: Combine like terms on the left-hand side: \[ (12x^2 + 6x) + (16x^2 – 8x) = 28x^2 – 2x \\ 28x^2 – 2x = 28x^2 – 7 \]Step 5: Transpose terms: \[ -2x = -7 \\ x = \frac{7}{2} \]Answer:x = \(\frac{7}{2}\)


Q14: Solve \(\frac{3}{x-2} – \frac{2}{x-3} = \frac{4}{x-3} – \frac{3}{x-1}\)

Step 1: Write the given equation: \[ \frac{3}{x-2} – \frac{2}{x-3} = \frac{4}{x-3} – \frac{3}{x-1} \]Step 2: Bring like terms together: \[ \frac{3}{x-2} + \frac{3}{x-1} = \frac{4}{x-3} + \frac{2}{x-3} \]Step 3: Simplify both sides: \[ \frac{3}{x-2} + \frac{3}{x-1} = \frac{6}{x-3} \]Step 4: Take LCM of the left-hand side \((x-2)(x-1)\): \[ \frac{3(x-1) + 3(x-2)}{(x-2)(x-1)} = \frac{6}{x-3} \]Step 5: Simplify the numerator: \[ 3(x-1) + 3(x-2) = 3x -3 + 3x -6 = 6x -9 \\ \frac{6x – 9}{(x-2)(x-1)} = \frac{6}{x-3} \]Step 6: Cross multiply: \[ (6x – 9)(x-3) = 6(x-2)(x-1) \]Step 7: Expand both sides:
LHS: \(6x(x-3) – 9(x-3) = 6x^2 -18x -9x +27 = 6x^2 -27x +27\)
RHS: \(6(x^2 -3x +2) = 6x^2 -18x +12\)
Step 8: Subtract RHS from LHS: \[ 6x^2 -27x +27 – (6x^2 -18x +12) = 0 \\ -9x +15 = 0 \]Step 9: Solve for x: \[ -9x = -15 \\ x = \frac{15}{9} = \frac{5}{3} \]Answer:x = \(\frac{5}{3}\)


Q15: Solve \((z+3)(z-3) – z(z+5) = 6\)

Step 1: Write the given equation: \[ (z+3)(z-3) – z(z+5) = 6 \]Step 2: Expand both terms using distributive property: \[ (z+3)(z-3) = z^2 – 9 \\ z(z+5) = z^2 + 5z \]Step 3: Substitute back into the equation: \[ (z^2 – 9) – (z^2 + 5z) = 6 \]Step 4: Simplify the left-hand side: \[ z^2 – 9 – z^2 – 5z = 6 \\ -5z – 9 = 6 \]Step 5: Solve for z: \[ -5z = 6 + 9 \\ -5z = 15 \\ z = -3 \]Answer:z = -3


Q16: Solve \(y(2y+3) – 2y(y-5) = 26\)

Step 1: Write the given equation: \[ y(2y+3) – 2y(y-5) = 26 \]Step 2: Expand the brackets: \[ 2y^2 + 3y – 2y^2 + 10y = 26 \]Step 3: Combine like terms: \[ (2y^2 – 2y^2) + (3y + 10y) = 26 \\ 13y = 26 \]Step 4: Solve for y: \[ y = \frac{26}{13} = 2 \]Answer:y = 2


Q17: Solve \(\frac{x+6}{4} – \frac{5x-4}{8} + \frac{x-3}{5} = 0\)

Step 1: Write the given equation: \[ \frac{x+6}{4} – \frac{5x-4}{8} + \frac{x-3}{5} = 0 \]Step 2: Take LCM of 4 and 8 for the first two terms: LCM = 8 \[ \frac{2(x+6) – (5x-4)}{8} + \frac{x-3}{5} = 0 \]Step 3: Simplify the numerator: \[ 2x + 12 – 5x + 4 = -3x + 16 \\ \frac{-3x + 16}{8} + \frac{x-3}{5} = 0 \]Step 4: Take LCM of 8 and 5 = 40 \[ \frac{5(-3x + 16) + 8(x-3)}{40} = 0 \]Step 5: Simplify the numerator: \[ -15x + 80 + 8x – 24 = -7x + 56 \\ \frac{-7x + 56}{40} = 0 \]Step 6: Set the numerator = 0: \[ -7x + 56 = 0 \\ -7x = -56 \\ x = 8 \]Answer:x = 8


Q18: Solve \(\frac{3}{4}(7x-1) – \left(2x – \frac{1-x}{2}\right) = x + \frac{3}{2}\)

Step 1: Expand the first term: \[ \frac{3}{4} \cdot 7x – \frac{3}{4} \cdot 1 = \frac{21x}{4} – \frac{3}{4} \]Step 2: Simplify the second term: \[ 2x – \frac{1-x}{2} = 2x – \frac{1}{2} + \frac{x}{2} = 2x + \frac{x}{2} – \frac{1}{2} = \frac{5x}{2} – \frac{1}{2} \]Step 3: Substitute back into the equation: \[ \frac{21x}{4} – \frac{3}{4} – \left(\frac{5x}{2} – \frac{1}{2}\right) = x + \frac{3}{2} \]Step 4: Distribute the negative sign: \[ \frac{21x}{4} – \frac{3}{4} – \frac{5x}{2} + \frac{1}{2} = x + \frac{3}{2} \]Step 5: Convert \(\frac{5x}{2}\) to \(\frac{10x}{4}\) and \(\frac{1}{2}\) to \(\frac{2}{4}\) for LCM: \[ \frac{21x}{4} – \frac{10x}{4} – \frac{3}{4} + \frac{2}{4} = x + \frac{3}{2} \\ \frac{11x}{4} – \frac{1}{4} = x + \frac{3}{2} \]Step 6: Multiply both sides by 4 to eliminate denominators: \[ 11x – 1 = 4x + 6 \]Step 7: Solve for x: \[ 11x – 4x – 1 = 6 \\ 7x – 1 = 6 \\ 7x = 7 \\ x = 1 \]Answer:x = 1



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