Answer:
Explanation:
You want the measures of x and ∠ECB in rectangle ABCD with center point E and AE=3x+6, BD=5x+19, ∠EBA=25°.
Diagonals
The diagonals of a rectangle are congruent and cross at their midponts. This means the triangles they form are all isosceles.
X
The value of x can be found by relating the length of a half-diagonal to the length of the whole diagonal.
2·AE = BD
2(3x +6) = 5x +19 . . . . . . . substitute given lengths
6x +12 = 5x +19 . . . . . eliminate parentheses
x = 7 . . . . . . . . . . . subtract 5x+12
The value of x is 7.
Angle
Angle EBC is the complement of angle EBA, so its measure is ...
∠EBC = 90° -∠EBA
∠EBC = 90° -25° = 65°
Angle ECB is the other base angle of isosceles triangle BCE, so has the same measure as ∠EBC.
∠ECB = 65°
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Additional comment
You know the corner angles of a rectangle are 90°, which is what makes angles EBA and EBC complementary.
With x = 7, AE = 27 and BD = 54. The full diagonal is double the length of the half-diagonal, as you expect.
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