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Because, in order for the equation to cross the x-axis (for example), the y-value must logically be zero. Otherwise the point that you find would not be along the x-axis; e.g if y=1, the point would be above the x-axis, or if y=-2, the point would be below the x-axis, rather than the intercept on the x-axis.

I.e to plot co-ordinates, you always plot x (across), the y (up or down). To find the x intercept, you need to know how much "across" it is, but you don't want it to be "up or down", since then it won't be the intercept. This is why 'y' must be zero.

The argument is the same for plotting y-axis intercepts.

Q: Why do you replace y or x with zero in equations that you use x and y intercepts?

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The Quadratic formula in mathematics is used to solve quadratic equations in algebra. The simplest way to solve these equations is to set each of the factors to zero and then solve each factor separately.

The x intercepts are when y=0. Substitute the zero in for all y and then solve. Use quadratic formula and reduce. I got (-1+/- sqrt 10)3 about .72075922 and -1.387425887

They use rational equations for fun in the evening to relax.

To solve two simultaneous equations - usually two equations with the same two variables each - you can use a variety of techniques. Sometimes you can multiply one of the two equations by a constant, then add the two equations together, to get a resulting equation that has only one variable. Sometimes you can solve one of the equations for one variable, and replace this variable in the other equation. Once again, this should give you one equation with a single variable to be useful.

well, if you know all the formulating equations it will make you better at regular equations and regular equations can be used in everyday life

Related questions

Graph the equation then find the x intercepts.

The vertex must be half way between the two x intercepts

The Quadratic formula in mathematics is used to solve quadratic equations in algebra. The simplest way to solve these equations is to set each of the factors to zero and then solve each factor separately.

The x intercepts are when y=0. Substitute the zero in for all y and then solve. Use quadratic formula and reduce. I got (-1+/- sqrt 10)3 about .72075922 and -1.387425887

If the slopes are different the lines are neither - they intersect. They are parallel or coincident if the slopes are the same. Then, if the y-intercepts are the same they are coincident while if the y-intercepts are different, they are parallel.

You can use a graph to solve systems of equations by plotting the two equations to see where they intersect

They use rational equations for fun in the evening to relax.

its easier

a system of equations

To solve two simultaneous equations - usually two equations with the same two variables each - you can use a variety of techniques. Sometimes you can multiply one of the two equations by a constant, then add the two equations together, to get a resulting equation that has only one variable. Sometimes you can solve one of the equations for one variable, and replace this variable in the other equation. Once again, this should give you one equation with a single variable to be useful.

well, if you know all the formulating equations it will make you better at regular equations and regular equations can be used in everyday life

There are people who use this web site that can and will solve equations.