a) expand and simplify: (4x-3)(x+1)

Question

i get 4x^2+x-3 ?

b) factorise: 2x^2 + 13x + 15

c) find y-int, x-int and vertex of:
y= x^2-3x-4

i get y-int = -4, but loose it from there :(

Answer 1

A. correct
B. look for two numbers m,n such that mn=2*15=30, and m+n=13.
m and n are therefore 10 and 3.
2x²+10x + 3x+15
=2x(x+5) + 3(x+5)
=(2x+3)(x+5)

C. y-intercept: correct.

X-intercept=zeroes.
Factorize y=x²-3x-4=(x+1)(x-4) to get the zeroes.

The vertex is located at x=-b/2a=-(-3)/2=1.5
and corresponding y is f(1.5)=-6.25

The vertex can also be found by completing the square.