BOOK OF MATHEMATICAL PROBLEMS. 



7G. Prove that 



(ab + ccl) (g* + 6- c'- d*) -(ac + bd) (a 2 - 6 2 + c 2 



77. Prove that 



a; + y + #2/3 



II. Equations. 

 78. Solve the equations 



(1) (x+ 1) ( + 2) (a; + 3) - (a> + 4) (x + 5) (x- 3), 



(2) (x + 1) (x+ 2) (aj+ 3) = (a:- 1) (aj- 2) (a-3) 



+ 3(4oj- 



(3) (x + a)(x + a +b) = (x + b)(x + 3a), 



m _L + _1_ = J_ + J_ 

 v ' # + 1 x + 5 x + 3 x + 7' 



< 5) _^ + * + . .j_. 



~ ' ' A " a; uC& X + 4(1 X + Clt 



() -+-4- 



a;+ 6 a a; + 6 c 



(7) 



x + 6 4- c a;-f a c 



(-V 



"T" "71 T 7i * 



= 0, 



