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Secondary School Mathematics for Class 10, 304, 17. /3, /3, 18., 2., 19. }, 13, 9,, 7.1 8., 20. (1) ВC 10 ст, (ii) AB 10/3 cm, 21. (i) AB 6/3 cm (ii) AC 12 cm, (ii) AB 3 cm, 23. ZA ZB 45°, 22. (i) BC 3 cm, 1, 24. ZA 45, 2B 15 25. ZA = 45", ZB=15 26., /3+1), (ii), 2/2, (/3+1), 27. (i), 2/2, HINTS TO SOME SELECTED QUESTIONS, 20. Let BC x cm. Then,, sin 30, ", X 10., 20, AB? = (AC2-BC?) = (20)²- (10)²) cm2 = 300 cm2 > AB /300 cm 10/3 cm., BC 10 cm and AB 10/3 cm., 21. Let AB x cm. Then, cot 30 /3 x6/3., AC2= (AB² + BC?) = ((6/3)2 + (6)?1 cm?= (108 +36) cm² = 144 cm² » AC = 12 cm., sin 45 5, 3/2, 22. Let BC x cm. Then,, X 3,, 12, AB, tan 45° 1, AB, =>, 3 cm, -1 AB 3 cm., BC, 23. sin (A+B)1 sin (A+B) sin 90,, cos (A-B) 1=cos (A-B) cos 0., Solve A+B 90", A-B 0" for A and B., 24. sin (A-B) sin (A-B)-sin 30"., cos (A+B) = cos (A+B)= cos 60., Solve A-B 30" and A+B 60" for A and B., 25. tan (A-B), tan (A-B)= tan 30"., tan (A+B) /3 tan (A+B)=tan 60"., Solve A-B 30 and A+ B 60 for A and B., 26. Adding, we get 3(x+)- (cosec 0+ cot 0)., Subtracting, we get 3(x-)-(cosec 9, 2/6