t=1时,s=13
13=uo+1/2a
t=2时,s=42
42=2uo+1/2a*4 (2)
13=uo+1/2a 两边同时乘上2得
26=2uo+a
a=26-2uo
代入(2)
42=2uo+1/2*(26-2uo)*4
42=2uo+52-4uo
uo=5
a=26-2uo=26-10=16
t=3时
s=5*3+1/2*16*3^2
=15+72
=87
4/3a^4b^7÷(-1/3ab^3)^2+1/2a^3b^8÷(-1/9a^2b^6),
=4/3a^4b^7÷1/9a^2b^6-1/2a^3b^8÷(1/9a^2b^6)
=12a^2b-9/2ab^2
将a=1/2,b=-4 代入得
12*(1/2)^2*(-4)-9/2*(1/2)(-4)^2
=-12-36
=-48