For what value of $y$ does the triangle with vertices $A(2, 7)$,$B(4, y)$,and $C(-2, 6)$ form a right angle at $A$?

In an isosceles triangle,the ends of its base are $(2a, 0)$ and $(0, a)$. One of its two other sides is a horizontal line (not the $X$-axis). If the third vertex is $(x_1, y_1)$,then $x_1 + y_1 =$

If the mid-points of the sides $BC$,$CA$ and $AB$ of a triangle $ABC$ are respectively $(2,1)$,$(-1,-2)$ and $(3,3)$,then the equation of the side $BC$ is

The sides $AB, BC, CD$ and $DA$ of a quadrilateral are $x + 2y = 3, x = 1, x - 3y = 4$ and $5x + y + 12 = 0$ respectively. The angle between diagonals $AC$ and $BD$ is ......$^o$

The points $(1,3)$ and $(5,1)$ are two opposite vertices of a rectangle. The other two vertices lie on the line $y = 2x + c$,where $c$ is a constant. The coordinates of the other two vertices are:

The perimeter of a triangle is $16 \text{ cm}$,and one of the sides is of length $6 \text{ cm}$. If the area of the triangle is $12 \text{ cm}^2$,then the triangle is: