а5=9 а1+4d=9 a1=9-4d a2+a9=20 a1+d+a1+8d=20 2a1+9d+20
2(9-4d)+9d=20 18-8d +9d=20 d=20-18 =2
Sn=(2a1+(n-1)d/2)*n S10=(2+18/2)*10 = 100
2^8 * 25^8 / 50^6 = (2*25)^8 / 50^6 = 50^8 / 50^6 = 50^*8 - 6) = =50^2 =2500
7 x3 + 5 x2 - 4x-3 x2-7 x3+9 =2x^2-4x+9
3p*5/6p* 4/5p2- 9/2p2+2p*3/4-3+2p3=2p^4+2p^3-4.5p^2+1.5p-3