根据句意和所给的首字母填空
① —W____ is your birthday?
—It's on April 8th.
②The t____ month of the year is December.
③J____ is the seventh month of the year.
④ —H____ birthday to you!
—Thank you.
⑤Do you want to come to my birthday p____?
若实数a、b、c、d满足矩阵等式ab021102=24cd,则行列式abcd的值为____ .
如图,已知AC⊥BC,BD⊥AD,AC与BD交于O,AC=BD.
求证:△OAB是等腰三角形.