Question 9

If $$x + y = 10$$ and $$xy = 4$$, then what is the value of $$x^4 + y^4$$?

Solution

So, $$x^2+y^2=\left(x+y\right)^2-2xy=10^2-8=92\ .$$

And $$x^2y^2=16$$

So, $$x^4+y^4=\left(x^2+y^2\right)^2-2x^2y^2=92^2-2\times16=8432\ .$$

B is correct choice.

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