To find the area of a rhombus, multiply the lengths of the two diagonals and divide by 2 (same as multiplying by 1/2): The sides and angles of a rhombus: The sides of a rhombus are all congruent (the same length.) Opposite angles of a rhombus are congruent (the same size and measure.)
A square has two perpendicular bisectors but a square is not a rhombus (because a rhombus does not have all four angles = 90. Oh, but wait, a rhombus is a square in the same way a rectangle is a square but not the other way around.
 
        
             
        
        
        
Answer:
First one is wrong. x should be 16.
Second one is not completely visible, so cannot say.
Step-by-step explanation:
In the last step, the divison by 4 yields:
x/16 = 1, so x = 16
 
        
             
        
        
        
Area is height time width, or in this case, 3(2x^2+3x+5), which is 6x^2+9x+15.