\(a,\left(x-9\right)^2-\left(x+5\right)^2\\ =\left[\left(x-9\right)-\left(x+5\right)\right].\left[\left(x-9\right)+\left(x+5\right)\right]\\ =-14.\left(2x-4\right)\\ Thay:x=1,5.vào:\\ -14.\left(2.1,5-4\right)=-14.\left(3-4\right)=-14.\left(-1\right)=14\)
a: A=x^2-18x+81-x^2-10x-25
=-28x+56=-28*1,5+56=56-42=14
b: B=36x^2-15x-84x+35-36x^2+12x-1
=-87x+34
Khi x=-5 thì B=87*5+34=469
a) \(\left(x-9\right)^2-\left(x+5\right)^2\)
\(=\left[\left(x-9\right)+\left(x+5\right)\right]\left[\left(x-9\right)-\left(x+5\right)\right]\)
\(=\left(x-9+x+5\right)\left(x-9-x-5\right)\)
\(=-14\left(2x-4\right)\)
Thay x=1,5 vào bt ta có:
\(-14\cdot1,5\cdot\left(2\cdot1,5-4\right)=14\)
b) \(\left(3x-7\right)\left(12x-5\right)-\left(6x-1\right)^2\)
\(=36x^2-15x-84x+35-36x^2+24x-1\)
\(=-87x+34\)
Thay x=5 vào bt ta có:
\(87\cdot5+34=469\)
