20.已知a、b表示两条不同的直线,α,β表示两个不同的平面,则下列命题正确的是( )
A. | 若α∥β,a∥α,b∥β,则a∥b | B. | 若a?α,b?β,a∥b,则α∥β | ||
C. | 若a⊥α,b⊥β,α⊥β,则a∥b | D. | 若a⊥α,b⊥β,a⊥b,则α⊥β |
19.若实数x,y满足$\left\{\begin{array}{l}{x-y+1≥0}\\{x+y≥0}\\{x≤0}\end{array}\right.$,则z=x+2y+a的最小值是2,则实数a的值为( )
A. | O | B. | $\frac{3}{2}$ | C. | 2 | D. | -l |
18.已知sin(x-$\frac{π}{4}$)=$\frac{4}{5}$,则sin2x的值等于( )
A. | $\frac{8}{25}$ | B. | $\frac{7}{25}$ | C. | -$\frac{8}{25}$ | D. | -$\frac{7}{25}$ |
17.若集合M={x|-2≤x≤2},N={x|x2-3x=0},则M∩N=( )
A. | {3} | B. | {0} | C. | {0,2} | D. | {0,3} |
14.已知函数f(x)=ex-1,g(x)=-x2+4x-3,若f(a)=g(b),则b的取值范围是( )
A. | $[2-\sqrt{2},2+\sqrt{2}]$ | B. | $(2-\sqrt{2},2+\sqrt{2})$ | C. | [1,3] | D. | (1,3) |
13.设f(x)=$\left\{\begin{array}{l}{x-3,x≥10}\\{f[f(x+5)],x<10}\end{array}\right.$,则f(6)的值为( )
A. | 8 | B. | 7 | C. | 6 | D. | 5 |
12.下列命题中,真命题是( )
0 250885 250893 250899 250903 250909 250911 250915 250921 250923 250929 250935 250939 250941 250945 250951 250953 250959 250963 250965 250969 250971 250975 250977 250979 250980 250981 250983 250984 250985 250987 250989 250993 250995 250999 251001 251005 251011 251013 251019 251023 251025 251029 251035 251041 251043 251049 251053 251055 251061 251065 251071 251079 266669
A. | ?x0∈R,ex<0 | |
B. | 若a,b∈R,a+b=0的充要条件是$\frac{a}{b}$=-1 | |
C. | 命题p:?x∈R,f(x)≥0,则?p:?x0∈R,f(x)<0 | |
D. | 命题“在△ABC中,若$\overrightarrow{AB}•\overrightarrow{BC}$<0,则△ABC为钝角三角形的逆命题为真命题 |