X^2-7x+12=0
X^2+8x+7=0
X^2+2x-15=0

х²-7х+12=0а=1; в=-7; с=12D = в²-4асD = (-7)² - 4*1*12= 49-48=1>0 - 2 корнях= -в+/-√D деленное на 2ах= -(-7) + √1 / 2*1=7+1/2=8/2=4х= 7-1/2=6/2=3Ответ.х= 4; 3