Question

Afla valoare lui X
a) 2+4+6+.....+98+X=1+2+3+4+5....+99

Answer 1

$a)2+4+6+8+...+98+x= \\ \\ 1+2+3+4+5+...+99= \\ \\ 99*100:2= \\ \\ 9900:2=4950$

$2+4+6+8+...+98= \\ \\ 2*(1+2+3+4+...+49)= \\ \\ 2*(49*50:2)= \\ \\ 2*1225=2450 \\ \\ x=4950-2450=2500$

Answer 2

a)
2+4+6+.....+98+X = 1+2+3+4+5....+99

2×(1+2+3+...+49) + X = 99 × 100 : 2

2 × 49 × 50 : 2 + X = 99 × 50

49 × 50 + X = 99 × 50

X = 99 × 50 - 49 × 50

X = 50 × ( 99 - 49)

X = 50 × 50

X = 50^2

X = 2 500