Help còn câu cuối cho a^3-3ab^2=2 b^3-3a^2b=11 Tính a^2+b^2

`a^3-3ab^2=2`

`(a^3-3ab^2)^2=2^2`

`a^6-2·a^3·3ab^2+(3ab^2)^2=4`

`a^6-6a^4b^2+9a^2b^4=4 (1)`

`b^3-3a^2b=11`

`(b^3-3a^2b)^2=11^2`

`(b^3)^2-2·b^3·3a^2b+(3a^2b)^2=121`

`b^6-6a^2b^4+9a^4b^2=121 (2)`

Cộng `(1)` cho `(2)` ,ta có:

`a^6-6a^4b^2+9a^2b^4+b^6-6a^2b^4+9a^4b^2=4+121`

`a^6+(-6a^4b^2+9a^4b^2)+(9a^2b^4-6a^2b^4)+b^6=125`

`a^6+3a^4b^2+3a^2b^4+b^6=125`

`(a^2)^3+3·(a^3)^2·b^2+3·a^3·(b^2)^2+(b^2)^3=125`

`(a^2+b^2)^3=5^3`

`a^2+b^2=5`