Bài 1:
a: \(D=\left(4x+3\right)\left(6x-2\right)-\left(3x-1\right)\left(8x+1\right)\)
\(=24x^2-8x+18x-6-\left(24x^2+3x-8x-1\right)\)
\(=24x^2+10x-6-24x^2+5x+1=15x-5\)
b: Khi x=8 thì D=15*8-5=120-5=115
c: D=10
=>15x-5=10
=>15x=15
=>x=1
Bài 2:
a: \(\left(a+b\right)\left(a-b\right)=a^2-ab+ab-b^2=a^2-b^2\)
b: \(\left(a+b\right)\left(a^2+2ab+b^2\right)-3ab\left(a+b\right)\)
\(=\left(a+b\right)^3-3ab\left(a+b\right)=a^3+b^3+3ab\left(a+b\right)-3ab\left(a+b\right)\)
\(=a^3+b^3\)
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