Hence, from (1), the square root required is— √ + (a + √ a2 - b) + √ ‡ (a − √ a2 − b). b) is a perfect square, our result is more complicated than the original expression, and therefore the above method fails in that case. Ex. 1. Find the square root of 14 + 6√5. ́ Squaring, then, 14 + 6√5 = x + y + 2√xy. .(1.) .(2.), .(3). 5. 180........ 9, y 9+ From these equations we easily find x = = 5 or 3+ 5. 1496. Hence, the square root required is √22 + 22, y = √17. 17. ( 21. The square roots of quantities of this kind may often be found by inspection. Ex. 1. Find the square root of 19 + 8 √3. We shall throw this expression into the form a2 + 2 ab + b2, which we know is a perfect square. Dividing the irrational term by 2, we have 4 √3. Now all we have to do is to break this up into two such factors that the sum of their squares shall be 19. The factors are evidently 4 and √3. Thus, we have 19 + 8√3 = (4)2 + 2 (4) √3 + (√3)2 = (4 + √√3)2. The square root is therefore 4 + √3. Ex. 2. Find the square root of 29 + 12√5. We have 29 + 12 √5 = (3)2 + 2 (3)2 √5 + (2 √5)2 Find the value of― 16. √12+ √48 - 2√3, √56 + 189. 19. a + ab + b by √ã - √b, a3 + bì by √ã - √b. 20. (x + y) by (x + y)3, a + b √d by a2 - ab √d + b2d. 22. a3 + b2 + c1 + d3 by a3 b3 + c3 - dt. Divide 28. 2 ys' √/2 + √3' x + xy + y Find the square roots of— 29. 11 + 4√7, 8 + 2 √15, 30 10 √√5. 30. 8+ 2 √12, 96 √2, 2010 √3: CHAPTER V. RATIO AND PROPORTION. Ratio. 22. The student is referred to Chapter II. of the Arithmetic section of this work for definitions and observations. which need not be repeated here. 23. A ratio of greater inequality is diminished, and a ratio of less inequality is increased, by increasing the terms of the ratio by the same quantity. be the ratio, and let each of its terms be It will then become a + m b + m a Hence the ratio is increased when ba, that is, when it is a ratio of less inequality; and is diminished when ba, that is, when it is a ratio of greater inequality. COR. It may be shown in the same way that— A ratio of greater inequality is increased, and a ratio of less inequality is diminished, by diminishing the terms of the ratio by the same quantity. 24. When the difference between the antecedent and consequent is small compared with either, the ratio of the higher powers of the terms is found by doubling, trebling, &c., their difference. 25. Proportion, as has been already said, is the relation of equality expressed between ratios. Thus, the expression a: b = c:d, is called a proportion. or ab:: cd, ... b :a::d: c (invertendo). Also, by Art. 64, page 214, we have- = (6.) a + b: a b c +d: c d (componendo and dividendo). 27. If a b::c:d and e:f::g: h, we may compound the proportions. |