We use sin in vector product and not using cosine because
Sin function is natural for physical process,
The value arise from zero to max
Hope this helps
a) For principal amount P, interest rate r, and number of years t, the amortization formula for the monthly payment A is ...
... A = P(r/12)/(1 -(1 +r/12)^(-12t))
... A = 22500·(0.06/12)/(1 -(1 +0.06/12)^(-12·20)) ≈ 161.20
The monthly payment is $161.20.
b) After 240 payments, the amount repaid is
... $161.20·240 = $38,688
c) (22500/38688)·100% = 58.2% is paid toward principal
The remaining amount, 41.8% is paid toward interest.
The width would be 16
4x22=88
1408-88= 1320
22x16x4= 1408
Answer : 64b^2 - 4
Hope that helps. If you need me to explain how I got my answer I will provide a picture.