web: add session1 web material

web/1_a

+Which of the following are valid R variable names?
+
+min_height
+max.height
+_age
+.mass
+MaxLength
+min-length
+2widths
+celsius2kelvin

web/1_b

+base_test <- function(x, base){
+  log_result <- logarithm(x, base=base)
+  exp_result <- base^log_result
+  test_result <- x == exp_result
+  return(test_result)
+}
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web/1_c

+base_test <- function(x, base){
+  print(x)
+  log_result <- logarithm(x, base=base)
+  print(log_result)
+  exp_result <- base^log_result
+  print(exp_result)
+  print(x)
+  test_result <- x == exp_result
+  return(test_result)
+}
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web/1_d

+base_test <- function(x, base){
+  print(x)
+  log_result <- logarithm(x, base=base)
+  print(log_result)
+  exp_result <- base^log_result
+  print(exp_result)
+  print(x)
+  test_result <- isTRUE(all.equal(x, exp_result))
+  return(test_result)
+}
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web/1_e

+base_test <- function(x, base){
+  return(isTRUE(all.equal(x, base^logarithm(x, base=base))))
+}
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