book Maths Puzzle Numerical Ability

I am having trouble getting problems into the quadratic form, for instance I don't undersatnd how to do put this problem into the right form.
(x+1)^2+2(x-2)=(x+1)(x-2)

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book Other Question

Find three consecutive even integers such that 3 times the sum of the first two is 48 less than the third. Write in algebraic symbols.

If one addend of x is c, what is the other addend