2.若$\sqrt{x-2y+9}$与|2x-y-3|互为相反数,则x-y的值为( )
| A. | -4 | B. | -2 | C. | 2 | D. | 4 |
20.下列各项中,去括号正确的是( )
| A. | x2-2(2x-y+2)=x2-4x-2y+4 | B. | -3(m+n)-mn=-3m+3n-mn | ||
| C. | -(5x-3y)+4(2xy-y2)=-5x+3y+8xy-4y2 | D. | ab-5(-a+3)=ab+5a-3 |
18.
如图,∠ABC=∠ACB,AD、BD、CD分别平分△ABC的外角∠EAC、内角∠ABC、外角∠ACF.以下结论:
①AD∥BC;
②∠ACB=2∠ADB;
③∠ADC=90°-∠ABD;
④∠BDC=$\frac{1}{2}$∠BAC.
其中正确的结论有( )
0 291061 291069 291075 291079 291085 291087 291091 291097 291099 291105 291111 291115 291117 291121 291127 291129 291135 291139 291141 291145 291147 291151 291153 291155 291156 291157 291159 291160 291161 291163 291165 291169 291171 291175 291177 291181 291187 291189 291195 291199 291201 291205 291211 291217 291219 291225 291229 291231 291237 291241 291247 291255 366461
①AD∥BC;
②∠ACB=2∠ADB;
③∠ADC=90°-∠ABD;
④∠BDC=$\frac{1}{2}$∠BAC.
其中正确的结论有( )
| A. | 2个 | B. | 3个 | C. | 4个 | D. | 1 个 |