№17
[tex] x^{2} +6x-7=0 \\ D=6 ^{2} -4*(-7)=36+28=64=8 ^{2} \\ \\ x_{1} = \frac{-6+8}{2} =1 \\ \\ x_{2} = \frac{-6-8}{2} =-7[/tex]
Answer: x₁ = 1
x₂ = - 7
№18
[tex]2 x^{2} -3x+4=3 \\ 2 x^{2} -3x+4-3=0 \\ 2 x^{2} -3x+1=0 \\ \\ D= -3 ^{2} -4*2=9-8=1 \\ \\ x_{1} = \frac{3+1}{2*2} = \frac{4}{4} =1 \\ \\ x_{2} = \frac{3-1}{2*2} = \frac{2}{4} =0.5[/tex]
Answer: x₁ = 1
x₂ = 0,5.
№19
[tex]2 x^{2} -4x-5=0 \\ D=-4 ^{2} -4*2*(-5)=16+40=56 \\ \\ x_{1}= \frac{4+ \sqrt{56} }{2*2} = \frac{4}{4} + \sqrt{ \frac{56}{16} } =1+ \sqrt{3.5} \\ \\ x_{2} = \frac{4- \sqrt{56} }{2*2} = \frac{4}{4} - \sqrt{ \frac{56}{16} } =1- \sqrt{3.5}
[/tex]
Answer: x₁ = 1 + √3.5
x₂ = 1 - √3.5
