Alan

Solve for (x,y) in the system of operations.

          2x + y = -7

            x = 4 + 2y

Collect the terms in x and y on the same side:

2x + y = -7       (1)

x - 2y = 4         (2)

Multiply the first equation by 2

4x + 2y = -14    (3)

Add (2) and (3) term by term:

5x = -10

so x = -2

Substitute this back into (1)

2*(-2) + y = -7

-4 + y = - 7

 y = -3

How can i calculate cosh with complex number?

There is one real solution and two complex solutions.  The real solution may be obtained as follows:

As follows:

Harriet has a square piece of paper.

She folds it in half to form a rectangle and then in half again to form a second rectangle (which is not a square).

The perimeter of the second rectangle is 30 cm

What is the area of the original square?

Set A has 10 more elements than set B. The two sets have 7 elements in common, and the total number of unique elements across both sets is 85.  How many elements set A have?

Derive as follows:

Solve as follows:

As follows:

The page numbers of a book sum to 1999. One page number was counted twice. Which page number was that?