Question

Factor completely: 2x2 − 8x − 42

Answer 1

first take out the common factor which is 2.
2(x^2 -4x - 21)
now look at the first and last term in the brackets
x^2 and -21
list the factors
x^2 (x,x) -21 (1,3,7)
and now for the last part, group them in brackets
2(x )(x ) <<last step
try to complete the last step.