semi-annual-compounding

Question 16.16: The six-month, 12-month, 18-month, and 24-month zero rates are 5%, 5.5%, 6%, and 6.5% (all measured with semi-annual compounding) respectively. What is the two-year par yield for a bond paying coupons every six months? For the par yield, I keep getting 6.41%, and A= 3.7465...

Hi! I'm confused about forward interest rate calculation, Hull (ch 4) uses RF=(R2T2-R1T1)/(T2-T1), Tuckman (ch 2) instead computes from formula (1+r(0,2)/2)^4=(1+r(0,1.5)/2)^3+(1+f(1.5,2.0)/2)^1. I'm sure the answer is just here but I can't see... Is it about compounding? Should I memorize both...