4х - 9х
При х=7
4*7-9*7=28-63= -35
При х=0,8
4*0,8-9*0,8=3,2-7,2= -4
(x-y)²-(x-y)(x+y)=x²-2xy+y²-(x²-y²)=
x²-2xy+y²-x²+y²=2y²-2xy
5c²d - 2c²d + c³d + 2c³d = 3c²d + 3c³d = 3c²d (1 + с )
8x^2+5x-4=0
D= 25-4*8*(-4)
D=153= 3Y17
x1,x2= (-5<u>+</u>3Y17)/16