Question

find roots of x²-3x-40=0 using factorisation method​

Answer 1

Answer: x = + 8, - 5.

Explanation: x^2 - 3x - 40 = 0

→ x^2 - (8 - 5)x - 40 = 0

→ x^2 - 8x + 5x - 40 = 0

→ x(x - 8) + 5(x - 8) = 0

→ (x - 8)(x + 5) = 0

Either, (x - 8) = 0 or, (x + 5) = 0

Either, x = + 8 or x = - 5.

More: Other methods include completing the square and the quadratic formula.

$x = \dfrac{- b \pm \sqrt{b^2 - 4ac}}{2a}$

Answer 2

xx - 3x - 40 = 0

xx - 8x + 5x - 40 = 0

x ( x - 8 ) + 5 ( x - 8 ) = 0

( x - 8 ) ( x + 5 )

x = 8 and x = - 5