а₁= 14, d= -5, S₄₀= ?
S₄₀ = (2а₁ +39d) * 40/ 2 = (2a₁ +39d)*20 = (2*14 +39*(-5)) * 20 = (28 - 195)*20=
=-167*20 = - 3340
1) \frac{42x-9 x^{2} +49}{42x}
2) \frac{1}{3x} - \frac{1}{7} = \frac{7-3x}{21x}
3) \frac{42x-9 x^{2} +49}{42x} : \frac{7-3x}{21x} = \frac{42x-9 x^{2} +49}{42x} * \frac{21x}{7-3x}
\frac{42x-9 x^{2} +49}{42x} * \frac{21x}{7-3x} = \frac{42x-9 x^{2} +49}{2(7-3x)}
(a+bi)+(c+di)=(a+c)+(b+d)i,
(a+bi)*(c+di)=(ac-bd)+(bc+ad)i,
=>
|d|=|b|, b=- d =>
a+c=10,
ac-bd=40,
d+b=0 =>
a+c=10,
ac+d^2=40, d=2,3,4,5,6
при d=3
a+c=10,
a*c=24,
=>
c^2-10c+24=0,
D=4
c1=6, a1=4, =>
число1=4-4*i
число2=6+4*i