Precalculus

Calculate the solution set.
x^2+y^2+8x=-15
9x^2+25y^2=225

My work:
I did elimination...multiplied -25 to the top equation and got..... -16x^2-200x-600...I then used quadratic formula ... And got -7.5 and -5.....
Is -7.5 an EXTRANEOUS SOLUTION because when I plugged -7.5 in for x in -16x^2-200x-600 the result does not equal to +600.

So then the answer is (-5,0) ?
Or is there another way to do this???
How can I check my answer by graphing?
Standard form and then graph it by shifting x and y starting the point of the center?

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  1. but I have
    -16 x^2 -200 x = 600
    so
    16 x^2 + 200 x + 600 = 0

    x = -7.5 or -5

    check -7.5
    16(7.5)^2 -200(7.5) +600
    900 - 1600 + 600
    zero, it worked for me

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    posted by Damon

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