# Solve

#### idontknow

$$\displaystyle \sqrt{x}=t$$.
The last digit of $$\displaystyle 169^{t} +144^{t}-2\cdot 156^{t}$$ must be $$\displaystyle 5$$.
The last digit of $$\displaystyle 169^{t} +144^{t}$$ or $$\displaystyle 9^{t}+4^{t}$$ must be $$\displaystyle 7$$ , which happens for $$\displaystyle t=2$$ or $$\displaystyle x=4$$.

https://brilliant.org/wiki/finding-the-last-digit-of-a-power/

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