How to make equality
Already from the first grade kids learn in math class concepts such as equality, the signs "more" and "less." On the job for years are becoming more complicated, but the requirement to make equality is found in them is also quite often as a sign of "equal" - the basis of any changes in mathematics.
Instruction create equality
If you are given the task, in which there is some condition that defines relations between the two unknown quantities, make equality based on it. Please mark one of the unknowns for x, then actuate these conditions. Equate the expressions obtained. Once you decide the equation, do not forget to inspect, substituting the values in the conditions of the problem. For example, you need to find the number of draining Petya, knowing that he has two sinks more than Vanya, and in the amount they sink 8. Designate for x number of plums Vanya, Petya will then be (x + 2). Total drain x + (x + 2), equating them to the condition specified in 8 plums, then choose the equation.
If the problem is based on the ratio of one quantity to another, make the equality of two relations, that is proportion. To do this, contrast the two values, for which we know that they correspond to each other. Designate the unknown, which is necessary to find, for x, and also contrast the the number of her, which by analogy must comply with it. As a result, you get a square of 4 numbers (one of them x), multiply the diagonal of the square, and equate to each other, and then choose the resulting equation.
For example, you know that 1 kg of dried apples obtained 140 grams of dried and it is necessary to know how many will turn out dried apples from 5 kg. Contrast between a "1 kg - 140 grams" (upper square line), since it is known that they directly correspond to each other. For x amount of dried apples, take out 5 kg of fresh. Thus, the bottom line of your square "5 kg - grams x." Multiply the diagonal of the square and make of them the equality: x = 1 * 140 * 5. Thus, x = 700 grams.
If you know at least two ways to find any parameter in the problem, make the equality of two different formulas. In this case it is not necessary, this parameter will be your goal, it only serves to equate the two expressions. For example, if you need to find the density of matter and at the same time you have been given its mass and dimensions, then proceed as follows: find the volume using the formula V = h * a * b (height, multiply the width and length), then make another formula volume: V = m / ρ. Equate the two expressions and express density.