While some feel that Thevenin's (commonly misspelled as Thevinin's) Theorem is made invalid by dependent sources, rather than independent sources, most hold his theories valid. This is largely due to the superposition theorem, proven by combining Thevenin's theorem with Norton's.
Because Thevenin does not work for a nonlinear network, e.g. a battery in series with a diode and resistor.
Because millman's is used in parallel ckt of impedances and voltage sources
A: THEVENIN theorem simply is a way to simplify a complex input and resistance to a simple form. maybe you are confusing it with nodal analysis
As we know that: The superposition theorem is that the linear responses in a circuit can be derived by summing the responses of the independent sources algebraically, therefore, it related to LINEAR CIRCUITS!
If this is an independent current source, it has to be disconnected.Independent voltage sources are replaced by a short-circuit.More about this at (see Related links):MasteringElectronicsDesign.com: How to Apply Thevenin's Theorem - Part 1, Solving Circuits with Independent SourcesandMasteringElectronicsDesign.com: How to Apply Thevenin's Theorem - Part 2. Nested Thevenin Sources Method
A: by using thevenin theorem
In circuits with multiple sources. This allows you to analyze the effects of each source separately, which often simplifies the math.
superposition can find the voltage and current effect of each source to a particular branch of the circuit and we can calculate the total effect of the sources to know the effect of the total sources to that branch
You are confusing "Thévenin" with "Theremin." Léon Charles Thévenin (1857-1926) developed a theorem for linear electrical networks stating that any combination of voltage sources, current sources and resistors with two terminals is electrically equivalent to a single voltage source and a single series resistor.
Norton's theorem is the current equivalent of Thevenin's theorem.
You cannot solve a theorem: you can prove the theorem or you can solve a question based on the remainder theorem.
There are 19 various aspects of Pythagoras theorem. Pythagorean Theorem (1) Pythagoras Theorem(2) Pythagorean Theorem (3) Pythagorean Theorem (4) Pythagoras Theorem(5) Pythagorean Theorem(6) Pythagrean Theorem(7) Pythagoras Theorem(8) Pythagorean Theorem (9) Hyppocrates' lunar Minimum Distance Shortest Distance Quadrangular Pyramid (1) Quadrangular Pyramid (2) Origami Two Poles Pythagoras Tree(1) Pythagoras Tree(2) Theorem by Pappus