LCM and HCF
-  What is the HCF of 8 (N5 - N3 + N ) and 28 (N6 + 1)?
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                        View Hint View Answer Discuss in Forum Let p(N) = 8 (N5 - N3 + N) 
 = 4 x 2 x N (N4 - N2 + 1)
 and q(N) = 28 (N6 + 1)
 = 7 x 4 [( N2)3 + (1)3]
 = 4 x 7 (N2 + 1) ( N4 - N2 + 1)Correct Option: ALet p(N) = 8 (N5 - N3 + N) 
 = 4 x 2 x N (N4 - N2 + 1)
 and q(N) = 28 (N6 + 1)
 = 7 x 4 [( N2)3 + (1)3]
 = 4 x 7 (N2 + 1) ( N4 - N2 + 1)
 ∴ HCF of p(N) and q (N) = 4 (N4 - N2 + 1)
-  The HCF of (x4 - y4) and (x6 - y6) is
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                        View Hint View Answer Discuss in Forum Let f (x) = (x4 - y4) 
 = (x2 - y2) (x2 + y2)
 = (x - y) (x + y) (x2 + y2)
 and g(x) = (x6 - y6)
 = (x3)2 - (y3)2
 = (x3 + y3) (x3 - y3)
 = (x + y) (x2 - xy + y2) (x - y)(x2 + xy + y2)
 = (x - y) (x + y) (x2 - xy + y2)
 (x2 + xy + y2)
 ∴ HCF of [f(x), g(x)] = (x - y) (x + y)
 = x2 - y2Correct Option: ALet f (x) = (x4 - y4) 
 = (x2 - y2) (x2 + y2)
 = (x - y) (x + y) (x2 + y2)
 and g(x) = (x6 - y6)
 = (x3)2 - (y3)2
 = (x3 + y3) (x3 - y3)
 = (x + y) (x2 - xy + y2) (x - y)(x2 + xy + y2)
 = (x - y) (x + y) (x2 - xy + y2)
 (x2 + xy + y2)
 ∴ HCF of [f(x), g(x)] = (x - y) (x + y)
 = x2 - y2
-  The HCF of (x3 - y2 - 2x) and (x3 + x2) is
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                        View Hint View Answer Discuss in Forum Let f(x) = x3 - y2 - 2x = x( x2 - x- 2) 
 = x( x2 - 2x + x - 2)
 = x {x (x - 2) + 1 (x -2)}
 = x (x +1) (x - 2)
 and g(x) = x3 + x2
 = x2 (x +1) = x. x (x +1)
 ∴ LCM of [ f(x), g(x)] = x (x +1) . x . (x - 2)Correct Option: CLet f(x) = x3 - y2 - 2x = x( x2 - x- 2) 
 = x( x2 - 2x + x - 2)
 = x {x (x - 2) + 1 (x -2)}
 = x (x +1) (x - 2)
 and g(x) = x3 + x2
 = x2 (x +1) = x. x (x +1)
 ∴ LCM of [ f(x), g(x)] = x (x +1) . x . (x - 2)
 = x2(x + 1)(x - 2)
 = x2(x2 - x - 2)
 = x4 - x3 - 2x2
-  What is the HCF of a2 b4 + 2 a2 b2 and (ab)7 - 4a2 b2?
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                        View Hint View Answer Discuss in Forum a2 b4 + 2 a2 b2 = a2 b2 ( b2 +2).......................(i) 
 and (ab)7 - 4 a2 b9 = a7 b7 - 4 a2 b9 = a2 b2(a5 b5 - 4b7)................(ii)
 from Eqs. (i) and (ii)
 HCF = a2 b2Correct Option: Ca2 b4 + 2 a2 b2 = a2 b2 ( b2 +2).......................(i) 
 and (ab)7 - 4 a2 b9 = a7 b7 - 4 a2 b9 = a2 b2(a5 b5 - 4b7)................(ii)
 from Eqs. (i) and (ii)
 HCF = a2 b2
-  Find the largest number which divides 1305, 4665 and 6905 leaving same remainder in each case. Also, find the common Remainder.
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                        View Hint View Answer Discuss in Forum Given that 
 x = 1305, y = 4665, z = 6905
 Then ,
 |x - y| = |1305 - 4665| = 3360
 |y - z] = |4665 - 6905| = 2240
 |z - x| =|6905 -1305| = 5600
 ∴ Required number = HCF of 3360, 2240 and 5600 = 1120
 On dividing 1305 by 1120, remainder is 185.
 On dividing 4665 by 1120, remainder is 185.
 On dividing 6905 by 1120, remainder is 185.
 ∴ Common remainder = 185Correct Option: CGiven that 
 x = 1305, y = 4665, z = 6905
 Then ,
 |x - y| = |1305 - 4665| = 3360
 |y - z] = |4665 - 6905| = 2240
 |z - x| =|6905 -1305| = 5600
 ∴ Required number = HCF of 3360, 2240 and 5600 = 1120
 On dividing 1305 by 1120, remainder is 185.
 On dividing 4665 by 1120, remainder is 185.
 On dividing 6905 by 1120, remainder is 185.
 ∴ Common remainder = 185
 
	