a) Hàm số trên nghịch biến trên R vì:

\(1< \sqrt{5}\Rightarrow1-\sqrt{5}< 0\) 

\(\Rightarrow\) hệ số \(a< 0\)

b) Khi \(x=1+\sqrt{5}\)

\(y=\left(1-\sqrt{5}\right)\left(1+\sqrt{5}\right)-1\)

\(y=1^2-\left(\sqrt{5}\right)^2-1\)

\(y=1-5-1\)

\(y=-5\)

c) Khi \(y=\sqrt{5}\) khi và chỉ khi:

\(\left(1-\sqrt{5}\right)x-1=\sqrt{5}\)

\(\Leftrightarrow\left(1-\sqrt{5}\right)x=1+\sqrt{5}\)

\(\Leftrightarrow x=\dfrac{1+\sqrt{5}}{1-\sqrt{5}}\)

\(\Leftrightarrow x=\dfrac{\left(1+\sqrt{5}\right)^2}{1-5}\)

\(\Leftrightarrow x=-\dfrac{3+\sqrt{5}}{2}\)

37 Unless you eat an apple a day, you won't stay healthy

38 Unless you stop wasting money, you will run out of it

39 If it isn't an emergency, don't call me

40 If James doesn't study harder, he won't pass the test

41 Unless Jane finishes her work before 6 pm, she won't dine out with her friends

42 Unless my brother stays healthy, he won't go travelling

43 If you don't listen attentively to the teacher, it is not easy to do these exercises

Bài đâu ạ?

\(25\sqrt{\dfrac{x-3}{25}}-7\sqrt{\dfrac{4x-12}{9}}-7\sqrt{x^2-9}+18\sqrt{\dfrac{9x^2-81}{81}}=0\left(x\ge3\right)\)

\(=25\sqrt{\dfrac{1}{25}.\left(x-3\right)}-7\sqrt{\dfrac{4}{9}.\left(x-3\right)}-7\sqrt{x^2-9}+18\sqrt{\dfrac{1}{9}.\left(x^2-9\right)}=0\)

\(=5\sqrt{x-3}-\dfrac{14}{3}\sqrt{x-3}-7\sqrt{x^2-9}+6\sqrt{x^2-9}=0\)

\(\Rightarrow\dfrac{1}{3}\sqrt{x-3}-\sqrt{\left(x-3\right)\left(x+3\right)}=0\Rightarrow\sqrt{x-3}-3\sqrt{\left(x-3\right)\left(x+3\right)}=0\)

\(\Rightarrow\sqrt{x-3}\left(1-3\sqrt{x+3}\right)=0\Rightarrow\left[{}\begin{matrix}\sqrt{x-3}=0\\1=3\sqrt{x+3}\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x=3\\x=-\dfrac{26}{9}\left(l\right)\end{matrix}\right.\)

Gọi chiều rộng và chiều dài lần lượt là a,b

Theo đề, ta có: a+b=98 và (a-2)(b+10)=ab+348

=>a+b=98 và 10a-2b=368

=>a=47 và b=51

a)P: AA×aa

 Gp A     a

F1: Aa

b)P Aa×AA

GP  A,a   A

F1: 1AA:1Aa

c)P: aa×aa

Gp  a      a

F1:  aa

d)P Aa×aa

Gp  A,a   a

F1: 1Aa:1aa

e)P AA×AA

Gp. A.    A

F1:  AA

bạn xem lại xem đề có cho kiểu hình ko nhé!

aa:7=bb

=>(11.a):7=11.b

=>11.a:11.b=7

=>a:b=7

vậy a=7;b=1