log2【√(4+√7)+√(4-√7)】求解!

log2【√(4+√7)+√(4-√7)】
求解!

原式=(1/2)*2log2[(4+√7)+(4-√7)]
=(1/2)log2[(4+√7)+(4-√7)]^2
=(1/2)log2[8+2√{(4+√7)·(4-√7)}]
=(1/2)log2[14]
log2(√14)