Question

Calculati A+B stiind ca A= 7 / 4*3+ 8 / 5*3 + ..............+ 20 / 17*3 (/= linie de fractie)
B=1 / 3*4 + 2 / 3*5 + 3 / 3*6 + .....................+ 14 / 3*17

Answer 1

a+b= 7/4*3+8/5*3+...+20/17*3+1/3*4+2/3*5+...+14/3*17
grupam primul termen din a cu primul din b
a+b= (7+1)/4*3+(8+2)3*5+...+(20+14)/3*17
a+b= 8/4*3+10/3*5+...+34/3*17
a+b=1/3(8/4+10/5+...+34/17)
a+b=1/3(2+2+...+2)
a+b=1/3*2*14
a+b=28/3