\(x^5+y^5=\left(x+y\right)^5-5x^4y-10x^3y^2-10x^2y^3-5xy^4\)
\(=\left(x+y\right)^5-5xy\left(x^3+2x^2y+2xy^2+y^3\right)\)
\(=\left(x+y\right)^5-5xy\left[\left(x^3+y^3\right)+2xy\left(x+y\right)\right]\)
\(=\left(x+y\right)^5-5xy\left[\left(x+y\right)\left(x^2-xy+y^2\right)+2xy\left(x+y\right)\right]\)
\(=\left(x+y\right)^5-5xy\left(x+y\right)\left(x^2-xy+y^2+2xy\right)\)
\(=\left(x+y\right)^5-5xy\left(x+y\right)\left[\left(x+y\right)^2-2xy-xy+2xy\right]\)
\(=\left(x+y\right)^5-5xy\left(x+y\right)\left[\left(x+y\right)^2-xy\right]\)
\(=a^5-5.6.a\left(a^2-6\right)\)
\(=a^5-30a^3+180a\)
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a) M = t(10 - 4t) - t2(2t - 5) – 2t + 5 tại t = 5 ;
