(-1/2㎡+3/2m+2)+20=(-1/2㎡+3/2m+4)+㎡(-㎡/2+3m/2+2)+20=(-㎡/2+3m/2+4)+㎡-㎡/2+3m/2+2+20=-㎡/2+3m/2+4+㎡2+20=4+㎡㎡=18m=±3√2