2x2 36 2x 6x 6SolutionHe has factorised 2x2 as 2x and x a

Solution

He has factorised 2x² as 2x and x and factorised -36 as -6 times 6. This is not the way to factorise a quadratic expression.

To factorise a quadratic, multiply the coefficient of x² and the constant term. So, here it is 2 times -36, which would equal to -72. Now split -72 in two factors such that their sum is +1, which is the coefficient of x. Two such factors in this case would be 9 and -8. Rewrite the quadratic as follows:

2x² +9x-8x-36

=(2x² +9x) -(8x+36)

= x(2x+9)-4 (2x+9)

=(x-4)(2x+9)

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