sin2x=cos(90-2x)=cos[2(45-x)]=1-2sin²(45-x)=1-18/25=7/25
1年后，利息1.98%x扣税后是1.98%x×(1-20%)=0.01584x所以本息合计x+0.01584x=1.01584x2年利息2×2.25%×(1.01584x)=0.0457128x扣税是0.0457128x×(1-20%)=0.03657024x
