Why does the author use Δ1 + Δ2 for C instead of just Δ2?

[fonseh]

Homework Statement

I know that when the 80kN act on B , the frame will be dispalced by Δ1 to the right .. When the 40kN act on C , the frame will be displaced Δ2 to the right ... Why the author use Δ1 + Δ2 for C ?

Homework Equations

The Attempt at a Solution

Is the author wrong ? I think the author should use Δ2 at C instead of Δ1 + Δ2 for C , am i right ? Δ1 can / cannot be the same as Δ2 [/B]

 

[haruspex]

The two horizontal loads are applied together. The author chooses to define Δ₂ as C's additional displacement beyond that of B.
Do you have an issue with an equation based on that?

 

[fonseh]

The two horizontal loads are applied together. The author chooses to define Δ₂ as C's additional displacement beyond that of B.
Do you have an issue with an equation based on that?

why The author chooses to define Δ₂ as C's additional displacement beyond that of B ? why can't the author define the displacement at C = Δ₂ only ??

 

[haruspex]

why The author chooses to define Δ₂ as C's additional displacement beyond that of B ? why can't the author define the displacement at C = Δ₂ only ??

If you follow through the equations, some of them turn out simpler with the author's choice. Whether it is simpler overall I have not tried to determine.