D=a3-a2=0.7,
S13= ((2a1+d(n-1))/2)*n, тогда
S13= ((2*(-0.5)+0.7*12)/2)*13= 3.7*13=48.1
..................,........
1)
5x = 12.5
x = 2.5
2)
2x = 5
x = 2.5
3)
4x - 7x + 2 = 17
-3x = 15
x = -5
√(49х) - √(16х) + √(25х) = √(7²х) - √(4²х) + √(5²х) = 7√х - 4√х + 5√х =
=√х*(7- 4+5)= 8√х