Math CentralQuandaries & Queries


Subject: Mathematics question need help
Name: Clara
Who are you: Student

Given x + 2y = -2 and x - 2y = 18, find:
a) x^2 - 4y^2
b) x^2 + 4y^2

We have two responses for you.

Hi Clara.

Try first solving each of the given equations for x, then you have two expressions that each equal x, so they must equal each other. That lets you eliminate x and you can solve for the value of y. Using this value of y in either of the given equations, you can find the corresponding x.

Now that you have x and y, just use their values to solve (a) and (b).

Stephen La Rocque.>

Hi Clara,

A great deal of algebra is pattern recognition. I tell my students it's like hearing the first bar of a song you haven't heard before but immediately knowing the group.

Look at the expression

x2 - 4y2

Does it look familiar? If not then expand and simplify

(x - 2y)(x + 2y)


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