... b + c ) + 4abc 13; t = 0,5 3a a + b + c = hay a f ( a , b, c ) f ( a , t , t ) = 3(a + b + c ) + 4abc 13 3(a + t + t ) 4at + 13 = 3(b + c 2t ) + 4a(bc t ) 2 = 3b + c = 2 2(b + c ... 0,25 y = x3 3(2m + 1) x + 6m(m + 1) x + y ' = x 6(2m +1 ) x + 6m(m +1 ) b) 0,5 y cú = ( 2m + 1) 4(m + m) = > x= m y' = x = m+ 0,25 Hm s ng bin trờn ( 2 ;+ ) y ' > x > m + m Cõu II a) ... 7l + ) 7 Xột 0,25 ú m, t , l Z b) Gii phng trỡnh : (3x + 1) x = x + x PT 2(3 x +1 ) x =10 x + x 2(3 x +1 ) x = 4(2 x 1) + x + x im 0,25 t t = x 1(t 0) Pt tr thnh 4t 2(3 x + 1)t + x + x...