Baby Maths

Baby Maths

Description

They claimed "any preschooler can solve this Maths quiz". I doubt so.

Please round the answer you got to 5 decimal places. The flag is cvctf{answer}. (e.g. cvctf{1.00000})

Link

Solution

Here is a brief walk through. (v means vector)

• From vAO=vAB+4vAC and the fact that vAO=vAB+vBO, we can get vBO=4vAC. This also implies BO is parallel to AC.
• Let ∠BCA=α, AC=x, then ∠OBC=∠OCB=α, OA=OB=OC=4x, ∠OAC=∠AOB=2α. Since OA=OB we know ∠OAB=90°-α.
• Solve triangle OAC, we can get the value of α using cosine law.
• sin(∠BAC)=sin(90°+α)=cos(α) is the answer.

Flag: cvctf{0.75000}