State and prove mid point theorem class 9
Asked by admin @ in Math viewed by 289 People
State and prove mid point theorem class 9th
Asked by admin @ in Math viewed by 289 People
State and prove mid point theorem class 9th
Answered by admin @
MidPoint Theorem Statement
The midpoint theorem states that “The line segment in a triangle joining the midpoint of two sides of the triangle is said to be parallel to its third side and is also half of the length of the third side.”
Step-by-step explanation:
Proof:
If the line segment adjoins midpoints of any of the sides of a triangle, then the line segment is said to be parallel to all the remaining sides, and it measures about half of the remaining sides.
Consider the triangle ABC,
Let E and D be the midpoints of the sides AC and AB. Then the line DE is said to be parallel to the side BC, whereas the side DE is half of the side BC; i.e.
DE II BC
DE = (1/2 * BC).
Construction
Extend the line segment DE and produce it to F such that, EF = DE.
In triangle ADE and CFE,
EC = AE ⇒ (given)
∠CEF = ∠AED (vertically opposite angles)
EF = DE (by construction)
By SAS congruence criterion,
Δ CFE ≅ Δ ADE
Therefore,
∠CFE = ∠ADE {by c.p.c.t.}
∠FCE= ∠DAE {by c.p.c.t.}
and CF = AD {by c.p.c.t.}
∠CFE and ∠ADE are the alternate interior angles.
Assume CF and AB as two lines that are intersected by the transversal DF.
In a similar way, ∠FCE and ∠DAE are the alternate interior angles.
Assume CF and AB are the two lines that are intersected by the transversal AC.
Therefore, CF ∥ AB
So, CF ∥ BD
and CF = BD {since BD = AD, it is proved that CF = AD}
Thus, BDFC forms a parallelogram.
By the properties of a parallelogram, we can write
BC ∥ DF
and BC = DF
BC ∥ DE
and DE = (1/2 * BC).
Therefore, the Midpoint theorem is proved.
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