Răspuns:
Explicație pas cu pas:
1.
(11x - 7) / (3x + 4) = 4/7
7(11x - 7) = 4(3x + 4)
77x - 49 = 12x + 16
77x - 12x = 49 + 16
65x = 65
x = 1
_____________
2.
2a + 4a + 6a +...+ 98a = a(2 + 4 + 6 + ... + 98)
a1 = 2; an = 98; r = 2
an = a1 + (n -1)r
98 = 2 + 2(n - 1) = 2 + 2n - 2 = 2n
n = 98 : 2 = 49 termeni in suma
2 + 4 + 6 + ... + 98 = 49*(2 + 98)/2 = 49*100/2 = 2450
2450a/42 = 175/3
a = 42*175/3*2450 = 7350/7350 = 1
