SOLUTION: Sum of square of two number is 80. One number is twice the other number. .find the number. Please help me..I need the answer 4. Please answer with full steps.

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Question 1022159: Sum of square of two number is 80. One number is twice the other number. .find the number. Please help me..I need the answer 4. Please answer with full steps.
Found 2 solutions by josgarithmetic, ikleyn:
Answer by josgarithmetic(39630) About Me  (Show Source):
You can put this solution on YOUR website!
Write the description symbolically:
system%28x%3Cy%2Cx%5E2%2By%5E2=80%2C2x=y%29

You solve that system? A simple substitution is the start:
x%5E2%2B%282x%29%5E2=80
Do you know what to do with this?

--
You might have just made a small arithmetic mistake.
x%5E2%2B%282x%29%5E2=80
x%5E2%2B4x%5E2=80
5x%5E2=80
x%5E2=16
x=-4 or x=4

and y=-8 or y=8, correspondingly.

Answer by ikleyn(52884) About Me  (Show Source):
You can put this solution on YOUR website!
.
Sum of square of two number is 80. One number is twice the other number. .find the number. Please help me..I need the answer 4. Please answer with full steps.
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Answer. The number is 4. The other number is 2*4 = 8.
        4%5E2+%2B+8%5E2 = 16 + 64 = 80.

        The other solution is -4. Then the other number is 2*(-4) = -8.
        Again, %28-4%29%5E2+%2B+%28-8%29%5E2 = 16 + 64 = 80.


Solution


Let x be the number under the question.
Then the second number is 2x. 
The condition requires that

x%5E2+%2B+%282x%29%5E2 = 80.

Simplify this equation:

x%5E2+%2B+4x%5E2 = 80  --->  5x%5E2 = 80  --->  x%5E2 = 80%2F5 = 16  --->  x = sqrt%2816%29 = +/- 4.