Câu 4(1đ): Khai triển và rút gọn biểu thức: P =( $(\sqrt{2} -\sqrt{5})^4$ + $(\sqrt{2}+\sqrt{5})^4$

`(sqrt2-sqrt5)^4=C_4^0*(sqrt2)^4+C_4^1*(sqrt2)^3*(-sqrt5)+C_4^2*(sqrt2)^2*(-sqrt5)^2+C_4^3*sqrt2*(-sqrt5)^3+C_4^4*(-sqrt5)^4`

`=4-8sqrt10+60-20sqrt10+25`

`=89-28sqrt10`

`(sqrt2+sqrt5)^4=C_4^0*(sqrt2)^4+C_4^1*(sqrt2)^3*sqrt5+C_4^2*(sqrt2)^2*(sqrt5)^2+C_4^3*sqrt2*(sqrt5)^3+C_4^4*(sqrt5)^4`

`=4+8sqrt10+60+20sqrt10+25`

`=89+28sqrt10`

`=>` `P=89-28sqrt10+89+28sqrt10=178`

Vậy `P=178`

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