Question

If (x + a)(x-3) = x2 + 2x - 15, what is the value of a ?​

Answer 1

x^2 - 3x + ax - 3a = x^2 + 2x - 15

x^2 - 3x + ax - 3a+3a = x^2+2x-15+3a

x^2-3x+ax=x^2+2x-15+3a

x^2-3x+ax-(x^2+2x)=x^2+2x-15+3a-(x^2+2x)

ax-5x=-15+3a

ax-5x

x(a-5)

a=5