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How to work out an integral with its limits in variables on a TI-84 Plus or TI-83 Plus

By E-Code · updated

Store the limits first (0 STO→ ALPHA A, 2 STO→ ALPHA B), then press MATH 9 for fnInt( and type fnInt(X²,X,A,B) and ENTER: 2.666…. Store new limits and run the same line again with 2nd ENTRY.

Step by step

  1. Lower bound in A. 0 STO→ ALPHA MATH Type 0, press STO→, then ALPHA and MATH for A: A holds the lower bound.
  2. Store it. ENTER Press ENTER.
  3. Upper bound in B. 2 STO→ ALPHA APPS ENTER Type 2, STO→, ALPHA and APPS for B, then ENTER: B holds the upper bound.
  4. Open MATH. MATH Press MATH. Item 9 is fnInt(, the definite integral.
  5. Pick fnInt(. 9 Press 9. fnInt( is pasted on the home screen.
  6. Function and variable. X,T,θ,n X² , X,T,θ,n , Type X,T,θ,n x² , X,T,θ,n , for the function X² and the variable X.
  7. The bounds as letters. ALPHA MATH , ALPHA APPS ) Type ALPHA MATH for A, a comma, ALPHA APPS for B, and ).
  8. Work it out. ENTER Press ENTER.
  9. Change the bounds. 2.666… is the integral of X² from A = 0 to B = 2. Store new values in A and B, then press 2nd ENTRY until the fnInt( line is back, and ENTER: no retyping.

What the screen shows

2.666… is the integral of X² from A = 0 to B = 2. Store new values in A and B, then press 2nd ENTRY until the fnInt( line is back, and ENTER: no retyping.

Look for 2.666666667 on the screen.

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