10+20+30+...+90
= (10+90) + (20+80) + (30+70) + (40+60) + 50
= 100 x 4 + 50
= 400 + 50
= 450
a) 15+45 .x= −715 b) 13+(34−𝑥)=(−0,5)2
c) (8x3+1)⋅(4x2−9)=0 d) 3x+2+2.3x−1=261
10+20+30+...+90
= (10+90)+(20+80)+(30+70)+(40+60)+50
= 100 + 100 + 100 + 100 +50
= 400 + 50
= 450