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When two variables are linked in direct variation, they can written in the form: where k is the constant of variation Direct Variation y = kx b. the equation linking x and y. If y varies directly to x, and y = 32 when x = 4, find; a. the constant of variation, k. sub in the given values 'opposite operation' to get k by itself ÷ y = y = kx = k × = k x ÷ b. the equation linking x and y. If y varies directly to x, and y = 20 when x = 8, find; a. the constant of variation, k. ÷ y = y = kx = k × = k ÷ x b. the equation linking a and b. If a varies directly to b, and a = 4 when b = 10, find; a. the constant of variation, k. Answer in decimal form, startfrom the units column! ÷ a = a = kb = k × = k ÷ b Direct variation graphs are always straight lines through (0, 0). The vertical axis is traditionallythe dependent variable,that is the subject of theequation. because in y = kx, zero times k always gives you zero e.g. y = kx Choose a pair of coordinates to sub into the formula. In this example we will use the y value from when x = 2. Hence, y = ÷ y = kx = k × = k x ÷ Gradient = Sub the given coordinateinto the formula. Hence, y = ÷ rise run y = kx = k × = k = x ÷ Sub the given coordinate into the formula. Answer in decimal form, startfrom the units column! Gradient = Hence, y = ÷ y = kx = k × = k rise run ÷ = x |