Question

Помогите пожалуйста!!! В алгебре не шарю

Answer 1

N1

$\left(a+5\right)\left(b-4\right)=\\=ab+a\left(-4\right)+5b+5\left(-4\right)=\\=ab-4a+5b-5\cdot \:4=\\=ab-4a+5b-20$

$\left(y-1\right)\left(y+3\right)=\\=yy+y\cdot \:3+\left(-1\right)y+\left(-1\right)\cdot \:3=\\=yy+3y-1\cdot \:y-1\cdot \:3=\\=y^2+2y-3$

$\left(5x-2\right)\left(3x+5\right)=\\=5x\cdot \:3x+5x\cdot \:5+\left(-2\right)\cdot \:3x+\left(-2\right)\cdot \:5=\\=5\cdot \:3xx+5\cdot \:5x-2\cdot \:3x-2\cdot \:5=\\=15x^2+19x-10$

N2

$\left(x+3\right)\left(x-7\right)-4x\left(5-2x\right)=\\=x^2-4x-21-4x\left(5-2x\right)=\\=x^2-4x-21-20x+8x^2=\\=9x^2-24x-21$

$\left(x-3\right)\left(3x+1\right)-\left(2x+3\right)\left(4x-1\right)=\\=3x^2-8x-3-\left(2x+3\right)\left(4x-1\right)=\\=3x^2-8x-3-8x^2-10x+3=\\=-5x^2-18x$

N3

$\left(x-4\right)\left(x+2\right)-\left(x-5\right)\left(x+6\right)=-x\\x^2+2x-4x-8-(x^2+x-30)=-x\\x^2+2x-4x-8-x^2-x+30=-x\\2x-4x-8-x+30=-x\\2x-4x-8+30=0\\-2x+22=0\\-2x=22|:(-2)\\x=11$