Question

Using the identity $(x+a)(x+b)=x^2+(a+b)x+ab$, find out the following product:
$(x+4)(x+7)$

Answer 1

using $(x+a)(x+b)=x^2+ba+(a+b)x$

For the above expression, keeping $a=4$ and $b=7$, we get

$(x+4(x+7)=(x^2+7\times 4+(7+4)x)=x^2+28+11x$