Question

Vreau sa imi rezolvati ex 2

Answer 1

S = 1 +3+ 5+ ........+(2x-1)  = 100
S1 = 2 + 4 + 6 + ......+ 2x   = 2( 1+2 +3+........+x) = 2·x(x+1)/2 = x(x+1)
S2 = S + S1 = 1+2+3+...........+2x = 2x(2x+1)/2 = x(2x+1)
S = S2 - S1 = x(2x+1) - x(x+1) = 2x² + x - x² - x = x²
x² = 100    x = 10
S = 1+ 3 +5+7+.......+ 19 = (1+19) + (3+17) +......+(9+11) = 20·5 =100