\(25-\left(x-y\right)^2=\left(5-x+y\right)\left(5+x-y\right)\)
\(a^4-1=\left(a^2-1\right)\left(a^2+1\right)=\left(a-1\right)\left(a+2\right)\left(a^2+1\right)\)
\(a,25-\left(x-y\right)^2\)
\(=5^2-\left(x-y\right)^2\)
\(=\left[5-\left(x-y\right)\right].\left[5+\left(x-y\right)\right]\)
\(=\left(5-x+y\right).\left(5+x-y\right)\)
\(b,a^4-1\)
\(=\left(a^2\right)^2-1^2\)
\(=\left(a^2-1\right)\left(a^2+1\right)\)
\(=\left(a-1\right)\left(a+1\right)\left(a^2+1\right)\)
Chúc bạn hok tốt!!!