(21x-9)(5+4x)=(4x+5)²
105x-45+84x²-36x=16x²+40x+25
84x²-16x²+69x-40x-45-25=0
68x²+29x-70=0
D=29² -4*68*(-70)=841+19040=19881=141²
x₁ = -29 -141 = -170 = -1.25
2*68 136
x₂ = -29+141 = 112 = 14
136 136 17
Ответ: -1,25; 14/17
B2.
x² +bx +2=0
D=b² -4*2 <0<br> b² -8<0<br>b² - 8=0
b² = 8
b=√8 b= -√8
+ - +
------- -√8 ---------- √8 --------------
\\\\\\\\\\\
b∈(-√8; √8)