(5v6-6v2)*(5v6-6v2)=25v36-30v12-30v12+36v4=25*6-60v12+36*2=150-60v12+72=222-60v12
v-корень
1)а7 = а1+6d; d=-4+8=4
a7=-8+6*4=16
S7= (a1+a7)/2 *7 = 28
1) 2x • x - 80 = -x^2 + 6x + 24+1
2x • x - 80 = -x^2 + 6x + 25
3x • x - 6x - 105 = 0
x^2 - 2x - 35 = 0
Дискриминант/4 = 1 + 35 = 36
x = 7; -5
Ответ: 7; -5