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We want to determine whether a function has a tangent which is horizontal. To answer the question we need to know what a horizontal tangent to a function means. A tangent to a graph of a function is a line w...

To see where the graph is greater than zero, we start by finding where it meets zero. By factorising (x^2 - 7x - 18), we find it equals (x-9)(x+2). The expression equals zero at the points x = 9 and x = -2. ...

Since y is equal to both 5-x and to x+1, we know that 5-x is equal to x+1. We can write 5-x=x+1. Take 1 away from each side: 4-x=x. Then add x to each side: 4=2x. Divide both sides by 2: 2=x. Now we have x, ...

Finding 51% of 400 is the same as finding 50% of 400, and 1% of 400, and adding them together. Finding 50% of a number is the same as finding half of the number, since half of 100% is 50%. Half of 400 is 200...

To solve this question, we need to use the chain rule, because the function is too complicated to solve simply by inspection. The chain rule says that dy/dx = dy/du × du/dx, where u is a function of x. In th...