【规定】\left|\begin{array}{ll}a& b\\ c& d\end{array}\right|=ad-bc.【理解】例如:\left|\begin{array}{ll}3& 2\\ 1& -3\end{array}\right|=3\times \left(\begin{array}{l}-3\end{array}\right)-2\times 1=-11.【应用】先化简,再求值:\left|\begin{array}{ll}xy-3{x}^{...
解:原方程组整理得\left\{ \begin{array}{l}{9a+6b+4c=80} \\ {a+b+c=15} \end{array} \right.,根据消元的思想将第二个式子扩大4倍相减后为:(9a+6b+4c)-4(a+b+c)=80-4×15,整理后得5a+2b=20,根据等式性质,2b为偶数,20为偶数,所以5a为偶数,所以a为偶数,当a=2时,5×2+2b=2...
解答解:由\left\{\begin{array}{l}x=-3+2cosθ\\ y=4+2sinθ\end{array}\left\{\begin{array}{l}x=-3+2cosθ\\ y=4+2sinθ\end{array},得{x+3=2cosθy−4=2sinθ{x+3=2cosθy−4=2sinθ,两式平方作和得,(x+3)2+(y-4)2=4; ...
解答 解:作出函数f(x)=\left\{\begin{array}{l}{{x^2}-2x,x≥-1}\\{x+4,x<-1}\end{array}}\left\{\begin{array}{l}{{x^2}-2x,x≥-1}\\{x+4,x<-1}\end{array}}的图象如图, 函数y=x+4 在 x∈(-∞,-1)上单调增,其值域为(-∞,3]; ...
解析 left ( ((begin(array)(ll) (1400=40k+b①) \ (3600=80k+b②) end(array))) right . ②-①,得:40k=2200 解之,得:k=55 把k=55代入①,得:1400=40times 55+b 解之,得:b=-800 therefore 方程组的解为:left ( ((begin(array)(ll) (k=55) \ (b=-800) end(array))) righ...
left ( 2 right )-left ( 1 right ),得 y=5. 把y=5代入left ( 2 right ),得 x-5=2. 解得 x=7. 所以方程组的解是left ( ((begin(array)(ll) (x=7) \ (y=5) end(array))) right ..反馈 收藏
left ( 4 right )-left ( 1 right )得: c=5 left ( 4 right )-left ( 2 right )得: b=3 left ( 4 right )-left ( 3 right )得: a=2 therefore left ( ((begin(array)(ll) (a=2) \ (b=3) \ (c=5) end(array))) right .反馈...
\left\{\begin{array}{l}x+2<3\\-2x<4\end{array}的解集是( ) A. -2<x<1 B. x<1 C. x>-2 D. x<-2试题答案 在线课程 分析 先求出两个不等式的解集,再求其公共解. 解答 解:{x+2<3①−2x<4②{x+2<3①−2x<4②由①得,x<1,由②得,x>-2,所以,不等式组的解集是-2<x...
13.若方程组$\left\{\begin{array}{l}{{a} {1}x+{b} {1}y={c} {1}}\\{{a} {2}x+{b} {2}y={c} {2}}\end{array}\right.$的解是$\left\{\begin{array}{l}{x=-2}\\{y=5}\end{array}\right.$.求方程组$\left\{\begin{array}{l}{2{a} {1}x-{b} {1}y={a} {1...
∵a*b=left(begin(array)l(a^b(a≤b,a≠0))\(b^a(a>b,b≠0))end(array)right.,(a-1)*(a-4)=1,∴(a-4)a-1=1,∴a-4=1或a-4=-1且a-1为偶数或a-1=0且a-4≠0,解得,a=5或a=3或a=1,故答案为:1或3或5.反馈 收藏 ...