当x=7时，2x—4.5=.{7z3d7b;j3[7L/q;`(X.J9w5\5q；当y=+k3y6G6h*k6L)r8s5o+m+C6^4d)Q时，4.A4V-y)u(B.i4[-m=12。.H5D7R