Tìm gtnn x^2-4x+25
Cho a,b,c,d,thỏa mãn a+b=c+d,a^2+b^2=c^2+d^2 CMR a^2013+b^2013=c^2013+d^2013
Tìm gtnn x^2-4x+25 Cho a,b,c,d,thỏa mãn a+b=c+d,a^2+b^2=c^2+d^2 CMR a^2013+b^2013=c^2013+d^2013
By Harper
By Harper
Tìm gtnn x^2-4x+25
Cho a,b,c,d,thỏa mãn a+b=c+d,a^2+b^2=c^2+d^2 CMR a^2013+b^2013=c^2013+d^2013
Giải thích các bước giải:
a.$x^2-4x+25=(x-2)^2+21\ge 21 \quad\forall x$
b.$a^2+b^2=c^2+d^2$
$\rightarrow a^2-c^2=d^2-b^2$
$\rightarrow (a-c)(a+c)=(d-b)(d+b)$
$\rightarrow a+c=d+b(a+b=c+d\rightarrow a-c=d-b)$
$\rightarrow a+c+(a-c)=d+b+(d-b)$
$\rightarrow 2a=2d$
$\rightarrow a=d$
$\rightarrow c=b$
$\rightarrow a^{2013}+b^{2013}=c^{2013}+d^{2013}$
$\rightarrow đcpm$