Bài 3: Những hằng đẳng thức đáng nhớ

H9
20 tháng 10 2023 lúc 19:40

a) \(\left(4x-5\right)^2\)

\(=\left(4x\right)^2-2\cdot4x\cdot5+5^2\)

\(=16x^2-40x+25\)

b) \(\left(-x+0,3\right)^2\)

\(=\left(-x\right)^2+2\cdot\left(-x\right)\cdot0,3+\left(0,3\right)^2\)

\(=x^2-0,6x+0,09\)

c) \(\left(-x-10y\right)^2\)

\(=\left(-x\right)^2+2\cdot\left(-x\right)\cdot\left(-10y\right)+\left(-10y\right)^2\)

\(=x+20xy+100y^2\)

d) \(\left(a^3-3a\right)^2\)

\(=\left(a^3\right)^2-2\cdot a^3\cdot3a+\left(3a\right)^2\)

\(=a^6-6a^4+9a^2\)

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NT
20 tháng 10 2023 lúc 19:40

a: \(\left(4x-5\right)^2=\left(4x\right)^2-2\cdot4x\cdot5+5^2=16x^2-40x+25\)

c: \(\left(-x+0.3\right)^2=\left(-x\right)^2+2\cdot\left(-x\right)\cdot0.3+0.3^2\)

\(=x^2-0.6x+0.09\)

d: \(\left(-x-10y\right)^2=\left(x+10y\right)^2\)

\(=x^2+2\cdot x\cdot10y+\left(10y\right)^2\)

\(=x^2+20xy+100y^2\)

e: \(\left(a^3-3a\right)^2\)

\(=\left(a^3\right)^2-2\cdot a^3\cdot3a+\left(3a\right)^2\)

\(=a^6-6a^4+9a^2\)

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