sin^2x+2sinxcosx-3cos^2x=12sinxcosx-4cos^2x=0sinxcosx=2cos^2xcosx（sinx-2cosx）=0（1）cosx=0,sinx=±1（2）sinx=2cosxtanx=2tan^x+1=51/cos^x=5cos^x=1/5sin^x=4/5sinx=±2√5/5