Answer:
40 classrooms
Step-by-step explanation:
Divide 1200 by 30.
1200÷30=40
If 390 students are boys just subtract 390 from 1200.
1200-390= 810
There must be 810 girls if there are 390 boys
Divide by 6

Square both sides

Simplify Left side using Trig identities: (Pythagorean, Double Angle)

Solve for x:
The equation of the line that is perpendicular to 4x - 3y = 10 through the point (-2,4) is 
<u>Solution:</u>
Given, line equation is 4x – 3y = 10
We have to find a line that is perpendicular to 4x – 3y = 10 and passing through (-2, 4)
Now, let us find the slope of the given line,

We know that, slope of a line
slope of perpendicular line = -1

Now, slope of our required line =
and it passes through (-2, 4)
<em><u>The point slope form is given as:</u></em>


Hence the equation of line is found out
A Quadrilateral A B C D in which Sides AB and DC are congruent and parallel.
The student has written the following explanation
Side AB is parallel to side DC so the alternate interior angles, angle ABD and angle BDC, are congruent. Side AB is equal to side DC and DB is the side common to triangles ABD and BCD. Therefore, the triangles ABD and CDB are congruent by SAS.
The student has also written
angles DBC and ADB are congruent and sides AD and BC are congruent. Angle DBC and angle ADB form a pair of alternate interior angles. Therefore, AD is congruent and parallel to BC. Quadrilateral ABCD is a parallelogram because its opposite sides are equal and parallel.
Postulate SAS completely describes the student's proof.
Because if in a quadrilateral one pair of opposite sides are equal and parallel then it is a parallelogram.