`(2ab + 5c)^2 + (ac - 10b)^2`
`<=> 4a^2b^2 + 20abc + 25c^2 + a^2c^2 − 20abc + 100b^2`
`<=> 4a^2b^2 + 25c^2 + a^2c^2 + 100b^2`
`<=> 4a^2b^2 + 100b^2+ 25c^2 + a^2c^2`
`<=> 4b^2(a^2 + 25) + c^2(25 + a^2)`
`<=> (4b^2 + c^2)(25 + a^2)`
$\text{@Sứa}$
$\text{Chúc bạn học tốt ^^ }$