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\(a^2+4b^2\)
\(=a^2+4ab+\left(2b\right)^2-4ab\)
\(=\left(a+2b\right)^2-4ab\)
\(=\left(a+2b-2\sqrt{ab}\right)\left(a+2b+2\sqrt{ab}\right)\)
\(4x^4+625=\left(2x^2\right)^2+\left(5^2\right)^2=\left(2x^2\right)^2+2.2x^2.5^2+\left(5^2\right)^2-2.2x^2.5^2\)
\(=\left(2x^2+25\right)^2-100x^2=\left(2x^2+25-10x\right)\left(2x^2+25+10x\right)\)
\(4x^4+625\)
\(=4x^4+20x^3-20x^3+50x^2+50x^2-100x^2-250x+250x+625\)
\(=\left(4x^4+20x^3+50x^2\right)-\left(20x^3-100x^2-250x\right)+\left(50x^2+250x+625\right)\)
\(=2x^2\left(2x^2+10x+25\right)-10x\left(2x^2+10x+25\right)+25\left(2x^2+10x+25\right)\)
\(=\left(2x^2+10x+25\right)\left(2x^2-10x+25\right)\)
\(x^4+y^4\)
\(=x^4+2x^2y^2+y^4-2x^2y^2\)
\(=\left(x^2+y^2\right)^2-\left(\sqrt{2}xy\right)^2\)
\(=\left(x^2+\sqrt{2}xy+y^2\right)\left(x^2-\sqrt{2}xy+y^2\right)\)
Ta có: \(\left(a+1\right)\left(a+2\right)\left(a+3\right)\left(a+4\right)-3\)
\(=\left(a+1\right)\left(a+4\right)\left(a+2\right)\left(a+3\right)-3\)
\(=\left(a^2+5a+4\right)\left(a^2+5a+6\right)-3\)
\(=\left(a^2+5a+5\right)^2-1-3\)
\(=\left(a^2+5a+5\right)^2-4\)
\(=\left(a^2+5a+7\right)\left(a^2+5a+3\right)\)
=a^4+4*a^2*b^2+4b^4-4*a^2*b^2
=(a^2+2b^2)^2-(2*a*b)^2
=(a^2+2b^2+2*a*b)*(a^2+2b^2-2*a*b)
=a^4+4*a^2*b^2+4b^4-4*a^2*b^2
=(a^2+2b^2)^2-(2*a*b)^2
=(a^2+2b^2+2*a*b)*(a^2+2b^2-2*a*b)